he goal of this project has been to enumerate, identify and haracterize genes uniquely expressed in B and/or T ymphocytes, with particular emphasis on those expressed at pecific stages of maturation, activation, or differentiation. hrough the use of subtractive cDNA-mRNA hybridization, cell-specific" cDNA probes and cDNA libraries have been btained. Such probes and libraries have thus far allowed the dentification, cloning, sequencing and understanding of enomic organization of the genes encoding 1) the -chain of the cell receptor and 2) the A class II MHC molecule. urthermore, this approach has allowed the identification of a amily of X chromosomal genes (XLR genes) uniquely expressed in ymphocytes. Among B lymphoma lines, presence of XLR mRNA orrelates with the stage of maturation. XLR genes are closely inked to the x-linked immunodeficiency (xid) gene of CBA/N ice; indeed xid may be a member of the XLR gene family.